C5 2.0 8v HDI MAF replaced fault still there

[THELABMAN]

Hi Folks,

I'd posted about an anti pollution fault on my C5 a week or so ago and after our moderator Richard kindly run it on his Lexia it was showing up faults on the MAF which I've just had replaced today but it's not cured the problem.

The garage I used doesn't have a Lexia but there diagnostic equipment at least can talk to my C5 and read all the faults which since everything has been cleared are showing up as follows :

Fault Code: P0235 - boost pressure sensor and Fault Code: P0110 - inlet air air temp sensor

Does anyone have any clue as to what these faults are exactly, where the sensors mentioned are located and the likely cost to buy and replace them ...

Regards

Peter

[RichardW]

that's a downer Peter....

The temp sensor is integral with the MAF and I'm pretty sure that I saw the boost sensor on top of the intercooler in front of the air box - all fed off that same cable that is chafed through... if that's the 5V reference line it could be pulling the voltage down to a point where the ECU throws a wobbly. Of course it could be a break in the line somewhere else, or it could be a fault in the underbonnet fuse box, or an ECU fault, or..., or.... How's your electrical fault finding?

The family are away for a few days on Saturday so if you want to interrogate it again, and maybe do a bit of fault finding, then I can probably manage at the weekend. The man for the job is probably Mandrake, but he's been very quiet of late....

[THELABMAN]

Hi Richard,

Funnily enough I thought the temp sensor might be located within the MAF as it does make sense to put it there.. the new unit is an aftermarket one from Eurocaparts and I'm just hoping it's ok and not faulty.... I'd a new intercooler fitted as the old one was leaking but the anti pollution warning had come on before it was replaced, I might try looking at it though and making sure all the connections seem ok.... I'm afraid that my fault finding skills, electrical of otherwise, are non existent.

I'm seriously tempted to contact the auto electrician who replaced my Coms unit to check it out, he does have a Lexia so has the proper tools for the job, and should certainly have the skills to replace or patch up this wIring properly ... the garage I've been to just stripped more back and wrapped it in insulating tape like you had done... the boost sensor is another £50 but I don't want to chuck money at it if that's not the issue....

[Peter.N.]

All the problems I have had on my C5 have been down to the pressure regulator on the back of the pump. Looks like this:

http://www.ebay.co.uk/itm/New-Common-Ra ... 461c0e19d0" onclick="window.open(this.href);return false;

Peter

[THELABMAN]

Hi Peter,

What fault codex where showing when you first started experiencing problems, I was getting an anti pollution fault warning on and when Richard ran his Lexia on the car it only showed up faults on the MAF.

I'd a new aftermarket unit fitted on Monday and since it's been replaced the MAF faults are gone however it's showing up faults on the boost pressure and inlet air temp sensor which the garage can't reset or clear as they keep coming back but nothing is showing for the MAF ...

Richard did notice a section of wiring that runs alongside the air intake trunking that had worn away exposing the copper wire which as it was intact he peeled back and sealed up with insulating tape and I think I really need to get this either repaired or at least confirmed that it's not the cause of the problem.

The other thing is that sometimes the fault clears on it's own and the car runs fine yet at others when it's showing the cars in a limp home mode and won't Rev above 2,800-3,000 RPM... I have noticed too though that after a run if the engine is stopped and restarted after say 10 mins that although the fault lights still on that the car runs fine throughout it's entire rev range .. This really confuses me .

I've spent a fair bit on the car recently, a lot more than it's actually worth to be honest, and would rather repair it and keep it than buy something else and end up fixing the same problems all over again but at the same time I'm loathe to throw money at it to replace parts that don't fix it and end up with car worth scrap value..

Peter

[Peter.N.]

It did various different things, the first was it was difficult to start when hot, then it went into limp home mode also the engine didn't stop straight away when you turned it off, the fault was there all the time though so the intermittent nature of your problem would suggest it was electrical.

Peter

[wheeler]

Check the little pipe on the bottom of the boost pressure sensor, it's a fine plastic nozzle that comes out of it onto a small rubber tube that connects to the intercooler. They are VERY easy to break when you remove the top of the air filter housing (which would likely have been removed to change the MAF sensor). They often get broken when changing air filters, telltale sign is usually a hissing noise when revving the engine. Worth a check.

[THELABMAN]

Hi Wheeler, I'd a look tonight when we'd got back from my wife's Aqua class and this looks ok it's certainly still attached to the rubber tube but this runs into a hose going to the intercooler and not directly into it.....

[THELABMAN]

Hi folks,

Quick update the auto electrician came out tonight and found a broken wire running to the Boost Pressure Sensor... a bit of solder to join it together with a heat shrink over it to protect it and touch wood the anti pollution and service light went out and all faults reset with car running fine and smooth again.... hopefully it stays this way.

I'd like to thank everyone for their input into likely cause and cures and especially to thank Richard for his initial Lexia Diagnostic session and the time taken to diagnose the initial issue as dodgy MAF unit..

Peter